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Thursday, January 24, 2013

The Coming Influenza Pandemic Part IV

In Parts I,
II and III I discussed the biology, morphology, etiology and genetics of
influenza and the various influenza pandemics that have occurred over the past
century. In Part IV I will discuss the social, political and economic factors
that influence influenza ecology and increase the likelihood and potential
severity of another deadly flu pandemic.

So far we
have dodged many bullets. There are several highly pathogenic avian strains
circulating among poultry and other fowl that cannot yet easily infect humans.
The number of these HPAI strains appears to be growing. There are several
socioeconomic factors that contribute not only to the proliferation of HPAI
strains, but also create opportunities for them to mix and reassort with human
and porcine strains. Further, some of these socioeconomic factors could make a
modern pandemic just as devastating, or worse, than 1918. These factors include
the growth of mega farms, in which tens of thousands of animals are crammed
into relatively small areas; the growth of mega slums, such as those found in
Mumbai and Nairobi, where hundreds of thousands of people live closely together
in squalor; the industrialization of Southern China, where mega farms and mega
slums collide with migrating water fowl that harbor novel influenza strains;
and the decline in public health and veterinary surveillance systems which can
monitor and quash outbreaks before they turn into pandemics.

Mega farms
are an enormous threat to public safety. They pollute the air, land and water
with animal wastes and they use up an inordinate amount of water. However, the
most dangerous aspect of mega farms may be the fact that so many animals are
cramped together that they easily spread diseases to each other, forcing farmers
to overuse antibiotics and other drugs to avert infections and massive
die-offs. This creates an ideal environment for genetic reassortment and
antigenic shift of influenza viruses.

20-30 years
ago, mega farms were relatively rare in the U.S. and virtually nonexistent in
the third world. Ranches typically had a few hundred or, if really large, a few
thousand head of cow or swine. The percentage of U.S. hogs raised on factory
farms with more than 5000 pigs has increased from 18% of all U.S. swine farms
in 1993 to 53% in 2003.3(p90)Western Arkansas and Northern Georgia, alone,
slaughter over one billion chickens per year.3(p83)One swine farm in Utah produces more raw
sewage than the entire city of Los Angeles.3(p84)The U.S. giant of poultry farming, Tyson,
slaughters more than two billion chickens per year in the U.S.3(p83)Mega farms are also starting to grow
throughout the world. Charoen Pokphond (CP), the Asian analog of Tyson, has
factory farms all over Thailand & China. CP won the very first permit to
operate a private enterprise in China, during the economic reorganization
initiated by Deng Xiaoping.3(p103-105) In 2003, during the height of a
Thai H5N1 outbreak, rather than cull their flocks, CP increased their rate of
slaughter and sent diseased chicken meat abroad3(p103-105)

During the
1918 Spanish Flu pandemic, the poor and hungry were the hardest hit, both in
morbidity and mortality.3(p28)Germany had a high mortality due to war
famine.3(p28)Iran was recovering from several years of
cholera, typhus, drought and famine, which contributed to the highest relative
influenza mortality (up to 22%) in the world.3(p29)India had a high mortality rate due to famine
and concurrent infection with malaria.3(p28)The pandemic hit India during harvest season,
exacerbating the famine. Today, the problem of poverty and famine may be worse.
In 1918, there were only 25 million slum dwellers worldwide. In 2005, there
were over 1 billion, and this is expected to double by 2020.3(p152)As you can see from the table below, some of the
world’s densest slums surpass the international average by almost two orders of
magnitude.

Poverty
affects health and immunity in several ways. Malnutrition deprives the body of
nutrients and calories necessary for homeostasis. Poverty creates uncertainty
about survival, which leads to stress and the overproduction of cortisol, which
can lead to diabetes, heart disease, hypertension, and impaired immune
response.16Poverty also forces people to live in
overcrowded conditions that facilitate the spread of germs. In many slums,
there may be as many as 1000 people sharing a single latrine.3Slum dwellers are less likely to have adequate
(if any) clean drinking water. They have less access to doctors and may be less
inclined to take stay home to recuperate from influenza for fear of losing income
or their jobs. People who are already ill are much more likely to contract and
die from influenza. This is even more true for those with compromised immune
systems. In Africa, 27 million people are infected with HIV. Combined with
poverty, malnutrition, and poor influenza surveillance and vaccination, Africa
will likely be hit hard by an influenza pandemic.3(p160)

Deforestation,
over-farming and overfishing have forced many subsistence workers to flee the
countryside for the cities throughout the developing world. These practices
also deprive people of protein in their diets and encourage the consumption of
exotic meats such as civets, in China, the hypothesized source of the SARS
virus, or monkeys, in Africa, the likely origin of HIV.3(p58)Deforestation, in particular, brings people in
closer contact with wild animals that may harbor novel diseases, such as Ebola.
In China, deforestation, over-farming, massive urbanization have led to
increased contact with flu carriers, such as wild water fowl in the Pearl River
Delta and increased genetic mixing between these vectors of influenza and
domesticated pigs, chickens and ducks.3

Influenza A
is endemic in ducks and geese from Siberia and Canada. As many as one-third of
young ducks and geese harbor the virus.3(p9)It infects their gut and is shed in their
feces into the same water they drink and from which they feed. It is usually
harmless to them, but it is spread rapidly, permitting considerable exchange of
genetic material.3(p9)One study in
Alberta found 27 different subtypes in one community of ducks.3(p9)During their migrations to the Gulf Coast and
southern China, they may continue to shed influenza for as long as one month.3(p9)

Siberian and
Canadian ducks and geese, which form the natural reservoir for influenza and
serve as vectors that transmit the disease to swine and people, fly south for
the winter, primarily to the Pearl River Delta, in Southern China. The Pearl
River Delta is one of the largest conglomerations of humans on Earth. It is
home to several large cities including Guangzhou (10 million), Shenzhen (8.4
million), Hong Kong (7 million), Dongguan (6.9 million), Foshan (6.7 million),
and three other cities of over 1 million people.14Macau is also located in the delta and has a
population density of more than 18,000 people per square kilometer.14Much of the region resembles Europe during
industrial revolution due to rapid industrialization. There are huge,
overcrowded slums, rampant pollution, poverty, all in close proximity to dense
poultry and swine farms. The percentage delta residents living in urban
settings grew from 32% in 1978 to 70% by 2002.3(p58-9)Air pollution in the delta is 24 times higher
than rest of China and 50% of the residents cannot afford medical attention
when ill.3(p58-9)

While
poverty is high, those who can afford meat are buying it more than ever
before.. This has led to the proliferation of wet markets (where live animals
are sold from cages), that serve as swap meets for influenza genes. Poultry
consumption in China more than doubled since 1980. There are 700 million
chickens in Guangdong province and many of the chicken cages sit atop pig pens,
allowing the pigs to eat infected chicken feces. 2003 study of the Guangdong
area found 500 different flu strains in wild & domestic birds (53 subtypes
of H9, alone).3(p62-63)

Stay tuned for Part V, tomorrow, when I will discuss how crumbling public health infrastructures also increase the chances of another deadly pandemic and the consequences.